Pipeline Design for Deepwater Gulf of Mexico Developments

ABSTRACT This paper discusses pipeline design for deep water Gulf of Mexico offshore developments. Hydrate formation, paraffin formation, well testing and slug flow are addressed. Remote subsea systems, floating production systems, and tension leg platforms are briefly explained, and the influence of each concept on pipeline design is discussed. A pipeline design for each development option is presented for an assumed "typical" deepwater Gulf of Mexico oil reservoir. The relative cost and merit of each option is discussed. The paper illustrates how reservoir producing characteristics influence pipeline design. Finally, conclusions specific to the example reservoir are presented. INTRODUCTION Offshore field developments are being planned for deep water Gulf of Mexico leases. Deep water is considered as a depth where conventional fixed platform facilities are no longer a viable solution for production of the field. For this paper, deep water will be water depths between 1500 and 3500 ft. Technology is currently available to develop reservoirs in this depth range. Subsea production systems (SPS) and tension leg platforms (TLP) are the most attractive technologiesfor deep water development in the Gulf. Compliant towers may have limited application for exploitation of large reserve reservoirs that require many wells (40 or more). This paper, however, will concentrate on the more typical 20-well Gulf of Mexico development scenario, so the compliant tower will not be discussed further. SPS and TLP both require sales pipelines to existing shallow water infrastructure. The design of these deep water lines is more complex than typical shallow water lines for the following reasons:Space and weight capacity are restricted and expensive on surface facilities located in deep water,Higher pressures and lower temperatures exist at the deep water seafloor,Divers are unable to work on the seafloor in deep water,The cost per mile for deep water pipelines is high. Multiphase pipelines have become increasingly attractive design alternatives over single-phase lines for deep water applications in the Gulf. Less processing equipment is required to send the produced fluids by multi phase pipeline to a shallow water 107ation for further processing. Reduced process equipment space and weight reduces initial capital cost Also, a multiphase system requires only one pipeline where a conventional system" requires two pipelines; one for the oil and one for the gas phase. Although several additional problems with the multiphase lines must be addressed, such as large pressure drop, hydrate formation,' slug flow etc., a single line system can have initial cost' advantages over a dual line system. New technologies have emerged in recent years that will impact deep water pipeline design. Multiphase pumps configured for both subsea and surface operation are in the testing phase. Multiphase metering devices are undergoing intensive development and are also reaching the test phase. Pilot subsea separators are being operated in the North Sea. Figure 1 shows the general location of the potential deep water developments in the Gulf of Mexico. The box shows the approximate region between the 1500 ft and 3500 ft water depth contours.